1. Field of the Invention
The present invention relates to a compound semiconductor device and a manufacturing method thereof. More specifically, the present invention relates to a compound semiconductor device having a mesa section formed by etching a compound semiconductor wafer, and a manufacturing method of such a compound semiconductor device.
2. Description of the Related Art
As conventional light emitting diode arrays each of which is manufactured on the basis of this compound semiconductor device and used in a data pack for printing a date in a camera, there have been known those described in, for example, Patent Literatures 1 to 4.
Patent Literature 1
Japanese Unexamined Patent Publication No. SHO 62(1987)-16583 (pages 2 to 4, FIGS. 1 to 4)
Patent Literature 2
Japanese Unexamined Patent Publication No. HEI10(1998)-335696 (pages 2 to 5, FIGS. 1 and 2)
Patent Literature 3
Japanese Unexamined Patent Publication No. HEI 3(1991)-190287 (pages 2 to 3, FIGS. 1 to 4)
Patent Literature 4
Japanese Unexamined Patent Publication No. HEI 8(1996)-64864 (pages 2 to 8, FIGS. 1 to 19)
According to the conventional art, when a semiconductor wafer having, for example, a Zinc Blend structure is obtained by liquid phase or vapor phase epitaxial growth, a substrate having a surface orientation in the vicinity of {100} is generally employed as a substrate for the epitaxial growth.
In the semiconductor wafer having the Zinc Blend structure, a {111} A surface and a {111} B surface greatly differ in etching rate due to the excess or deficiency of dangling bond. Therefore, in a case of obtaining a mesa shape by etching, when an etching rate is low, anisotropic etching is performed and a forward mesa surface and a backward mesa surface consequently appear. That is, a mesa surface in a forward direction (a mesa section side surface at an obtuse angle against a wafer surface from a direction parallel to a pair of two sides in a compound semiconductor device having the mesa section and obtained by subjecting a compound semiconductor wafer to a mesa etching and by isolating elements on two pairs of parallel sides) and a mesa surface in a backward direction (a mesa section side surface at an acute angle against the wafer surface) appear.
However, when the wafer having the mesa section thus formed on the surfaces is cut and isolated into a plurality of elements by means of dicing, the respective elements are often damaged by a coolant which cools a dicing blade. In other words, since the coolant is collided against the wafer surface at high speed by the dicing blade which rotates at high speed, the mesa section on the wafer surface is damaged, depending on the shape of the wafer surface against which the coolant is collided or the direction in which the coolant is collided against the wafer surface.
For example, when a thin film such as an electrode is formed on the mesa section, the thin film is often peeled off by collision pressure generated by the blade cooling coolant. To be specific, the conventional art has the following disadvantage. If the thin film (f) is formed on the mesa section on the surface of the wafer (w) as shown in FIG. 1 and the dicing blade (b1) rotates clockwise (cw), the thin film (f) tends to be peeled off on a part β. If the dicing blade (b1) rotates counterclockwise (ccw), the thin film (f) tends to be peeled off on a part α.
Even when no film is formed on the mesa section, crystals themselves are sometimes damaged by the collision pressure generated by the coolant. To be specific, the conventional art has the following disadvantage. If no film is formed on the mesa section on the surface of the wafer (w) as shown in FIG. 2 and the blade (b1) rotates clockwise (cw), a part δ tends to be damaged. If the blade (b1) rotates counterclockwise (ccw), a part γ tends to be damaged.
As can be seen, whether a film is formed on the mesa section or not, the peel-off or damage can be prevented to some extent by decreasing the quantity of the coolant or decelerating the rotational speed of the blade. However, these measures are not substantial solutions to these disadvantages. Further, if the measures are taken, not only the processing capability of a dicing machine deteriorates but also the rotational speed of the blade is decreased. As a result, a new defect resulting from cutting such as chipping may possibly occur.
Furthermore, even when a film is formed on the mesa section and the film is bonded to the mesa section strongly enough, a deformation such as the bending of the film may possibly occur. Besides, in an element inversion process for inverting the elements from one adhesive sheet, to which the wafer is fixed during the dicing process, onto another adhesive sheet, which process is performed after the element isolation by means of dicing, the film is sometimes peeled off on the upper portion of the mesa section or crystals are damaged on the lower portion of the mesa part at a location at which stress concentration on an acute part occurs.